1. Field of the Invention
This invention relates to a technique of fabricating a light guide used for a liquid crystal display, and more particularly to a light guide fabricating apparatus and a manufacturing method thereof having a simplified mold structure.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmissivity of liquid crystal cells arranged in a matrix pattern with the aid of a video signal applied thereto to display a picture corresponding to the video signal. To this end, the LCD includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix which control an amount of light transmitted from the lower portion thereof; a backlight unit for emitting light from the lower portion of the liquid crystal display panel; red, green and blue color filters corresponding to each liquid crystal cell at the lower portion of the liquid crystal display panel; and a black matrix layer for defining pixels. The backlight unit functions to evenly emit white light from the rear side of the liquid crystal display panel, and consists of a light source, a light guide, a reflector and a diffuser, etc. for uniformly transmitting light emitted from the light source into the panel.
FIG. 1 shows a sectional structure of a conventional backlight unit provided at the lower portion of a liquid crystal display panel. Referring to FIG. 1, the backlight unit includes a backlight lamp 22 for generating white light, a prism light guide 4 for guiding light passing through a light input 20 from the backlight lamp 22, a lamp housing 24 for mounting the backlight lamp 22 and reflecting light into the light guide 4, a reflector 2 for reflecting light from the lower portion of the prism light guide 4 toward the upper portion thereof where the liquid crystal display panel is positioned, first and second diffusing films 6 and 12, and first and second prism films 8 and 10 for controlling diffusion and transmission direction of the light passing through the prism light guide 4. The light guide 4 is formed in a prism shape with an inclined lower surface as shown in FIG. 2 and allows light inputted from the backlight lamp 22 to smoothly progress toward the upper portion thereof. Light transmission, via the lower surface of the prism light guide 4, toward the lower portion thereof is reflected upward by the reflector 2 provided at the lower portion of the light guide 4. Light passing through the prism light guide 4 is uniformly diffused by means of the first diffusing film 6. Light passing through the first diffusing film 6 is controlled to make its transmission direction perpendicular to the liquid crystal display panel at the first and second prism films 8 and 10. Light passing through the first and second prism films 8 and 10 is incident on the liquid crystal display panel by way of the second diffusing film 12 again.
For instance, the lower surface of the prism light guide 4 is inclined and provided with minute grooves 26 having a uniform distance as shown in FIG. 2. Such grooves 26 are referred to as xe2x80x9cprism unevennessxe2x80x9d, which smooths a diffusion of light as well and reduces light loss on a path where light is transmitted toward the upper portion of the light guide 4. This increases the amount of light transmitted toward the liquid crystal display panel. Typically, the prism light guide 4 is made from an acryl such as PMMA, etc., and the grooves 26 are formed in an equal distance to have a pitch width of about 0.07 to 0.08 mm by a machine working.
The prism light guide 4 having the structure as mentioned above is, for example, fabricated by an injection-molding device 30 as shown in FIG. 3. Referring to FIG. 3, the conventional light guide injection-molding device 30 consists of a stamper 32 for forming groves 26, a stationary core 34 to which the stamper 32 is attached, a vacuum tube 36 and a vacuum device (not shown) for attaching the stamper 32 to the stationary core 34 by a vacuum force, a stamper fixing segment 38 provided at the side portion of the stationary core 34 to determine an attached position of the stamper 32, a movable core 40 defining a mold 46 along with the stationary core 34, and a stationary molding plate 42 and a movable molding plate 44 for fixing the stationary and movable cores 34 and 40 at the exterior thereof. The stationary core 34 has a thickness of about 20 mm while the stamper 32 has a thickness of about 0.1 to 0.4 mm. In the conventional art, a brass plate (which is easy to work by a grinding process) is preferably used to make the stamper 32. Recently, a high-hardness nickel has been used because the relatively soft brass plate wears too easily, which affects mass production operation. However, since nickel is very hard, it is difficult to form the grooves 26 at an equal distance by a grinding process. In order to solve this problem, a nickel stamper 32 has been made by using a brass plate provided with the prism unevenness grooving as a master, then electroplating nickel on the surface of the brass plate provided with the prism unevenness grooving to a desired thickness. In manufacturing the stamper 32 according to the electroplating method, the stamper 32 has a thickness of about 0.1 to 0.4 mm because it is difficult to make a large plating thickness.
Hereinafter, a conventional method of fabricating the prism light guide 4 is described. First, a position of the stamper 32 to be attached to the stationary core 34 is determined by the stamper fixing segment 38. The stamper 32 is then attached to the attached portion of the stationary core 34. The portion of the stamper 32 attached to the stationary core 34 has a plurality of vacuum holes connected the vacuum tube 36. The stamper 32 is attached to the stationary core 34 by a vacuum force provided by evacuating air through the vacuum tube 36. Thereafter, a prism light guide material is injected into a space between the stationary core 40 and the stamper 32 and then injection-molded to be made into the prism light guide 4 having the prism unevenness grooves 26.
The conventional injection-molding device has a structure in which the stamper 32 is separate from the core 34 of the mold 46. The stamper 32 is temporarily attached to the stationary core 34 of the mold 46 by evacuating air through the vacuum holes provided at the attached portion of the stamper 32 to the stationary core 34. Such a stamper fixing method is mainly used for a product that must be changed frequently. In conventional compact disc injection-molding device (as an example of another application), various kinds of discs must be formed so various kinds of stampers must be changed frequently. Thus, the stamper fixing method employing a vacuum system is used in which attachment and detachment of the appropriate stamper is easy. However, the prism light guide 4 in the LCD is mass produced and therefore does not require frequent attachment and detachment of the stamper until a life of the stamper 32 expires. Therefore, the above-mentioned stamper attaching method using a vacuum system is not available. The conventional injection-molding device 30 has a drawback because it requires an additional device for evacuating air and the attached portion of the stamper 32 to the stationary core 34 must be provided with a plurality of vacuum holes, so device 30 has complex structure and facilities. Also, the conventional injection-molding device 30 unstable attachment due to a deterioration of the vacuum force applied to the stamper 32, its manufacturing becomes unstable. Furthermore, it is inconvenient because cleaning and fine surface grinding work, etc. on the attached portion of the stationary core 34 to the stamper 32 are required to provide an easy air evacuation and strengthen the vacuum force.
Accordingly, the present invention provides an apparatus for manufacturing a light guide in a liquid crystal display and a manufacturing method thereof wherein a mold structure is simplified.
The present invention also provides an apparatus for manufacturing a light guide in a liquid crystal display and a manufacturing method thereof that are adapted to make a stable light guide molding work.
Therefore, a light guide fabricating apparatus according to one aspect of the present invention includes a stamper for molding a light guide; a core material portion with a desired thickness fixed to the stamper, to constitute an integral molding core; and a fixing member or structure for fixing the stamper to the core material portion, said integral-type molding device defining a mold for molding the light guide along with the stationary core and the movable core.
A method of manufacturing a light guide fabricating apparatus according to another aspect of the present invention includes fixing a light guide molding stamper to a core material portion having a desired thickness to form an integral mold core; and fixing the integral mold core to the stationary core and the movable core to define a mold.